1. Field of the Invention
This invention relates to improvements in an epidark illumination system for use with a microscope.
2. Description of the Prior Art
A conventional epidark illumination system is shown in FIG. 1 of the accompanying drawing, wherein for enabling observation in a dark field of view within a reflection type microscope, a ring-shaped light flux 3 surrounding an objective 1 and having its center coincident with the optical axis of the objective is supplied from an unshown light source and such light beam is condensed upon a sample 2 by a ring-shaped condenser lens L1 disposed adjacent to the forward end of the objective.
The illumination system for a microscope must usually satisfy these requirements: (1) it must be bright; (2) it must be free of irregularity of illumination. The epidark illumination system for a dark field reflection type microscope must further satisfy the requirement; and (3) it must create no flare, that is, it must illuminate only the minimum necessary portion (real field of view). The conventional epidark illumination system has attempted to satisfy all the above three requirements by using a diffusing surface as at least one surface of the condenser lens L1 shown in FIG. 1. In such a case, the field of view provided may be free of irregularity of illumination to some extent, but the illuminating light is unnecessarily extensive even to a range beyond the observation field of view so that efficiency is low and not only is the illumination dark but also, as indicated by arrows in FIG. 1, the light rays outside the field of view are reflected by the surface of the sample and enter the objective to form a flare which seriously mars the contrast of the formed image. There has also been an arrangement which uses a metal mirror to condense the illuminating light, but this has not been satisfactory in that the reflection factor is low and the loss of light is great. Thus, the illumination systems as referred to above could not fully display their performance however excellent in performance the objectives therein were.